Large, two piece molds are desirably often moved with the respective two pieces, typically the mold core and the mold cavity, secured together. This, in turn, represents a potential safety hazard, requiring a reliable, foolproof lock to hold the mold halves together as they are lifted and transported. Should one attempt to lift such a mold system with a hook that is secured to only one of the mold halves, a fatal accident could occur if the other mold half falls out of engagement with the lifted mold half and lands on the floor. Even if no injuries are sustained by the accident, the damage to the mold half can run to many thousands of dollars.
Various mold locks have been proposed for addressing this safety issue. For example, see von Holdt U.S. Pat. Nos. 3,909,180; 4,004,448; 4,487,564; 4,702,456; 4,706,926; and 4,753,415.
Particularly referring to the latter cited U.S. Pat. No. 4,753,415, this simple mold lock structure utilizes a pair of bridges, each carried by one of the mold halves and adapted to be placed in abutting relation with the bridge of the other mold half. Thus, a lifting hook can lift both bridges at the same time, to lift both mold halves in a positively locked manner. The system is essentially foolproof, when no other means is provided on the mold for lifting, since the user is then forced to properly engage the hook with the two abutting bridges for safe lifting of the two mold halves together.
As one disadvantage of the aforesaid patent, the respective two bridges must be positioned at the parting line of the mold. If the parting line is not on the transverse center of gravity plane of the mold, the mold will tilt at an undesirable angle upon lifting with the hook, since it will be substantially off balance.
In accordance with this invention, a simplified, safe system is provided for lifting a pair of mold halves, preferably with a bridge positioned substantially on the center of gravity plane, even when the parting line of the mold is substantially spaced from the center of gravity plane. A center of gravity plane is defined to be that transverse plane through the mold at which the mass of the mold is equally spaced on both sides of the plane, so that lifting of the mold with a hook by means of a bridge spaced on such plane will cause the mold to be essentially balanced, to avoid radical canting thereof as it is lifted.